Reaction force isolation system

ABSTRACT

An exposure apparatus comprising an optical system for imaging a pattern formed in a reticle onto an article and a reticle stage for supporting the article. A motor is provided for positioning the reticle stage and reticle relative to the optical system and includes a first motor portion and a second motor portion. The first motor portion is connected to the reticle stage and movable relative to the second motor portion. The apparatus further comprises a vibration isolation device configured to isolate vibration resulting from reaction forces created between the first and second motor portions. A method of directing reaction forces created between the first and second motor portions is also disclosed.

FIELD OF THE INVENTION

[0001] The present invention relates generally to motor drivenpositioning systems, and more particularly, to a method and apparatusfor positioning and aligning a reticle or wafer in a photolithographysystem with a motor and isolating the system from reaction forces fromthe motor.

BACKGROUND OF THE INVENTION

[0002] Various support and positioning structures are available forpositioning an article for precision processing. For example, insemiconductor manufacturing, a wafer and reticle are preciselypositioned with respect to a photolithography apparatus. Planar orlinear motors are typically used to position and align the reticle andwafer for exposure in the photolithography apparatus. Conventionalplanar motors used in semiconductor manufacturing are disclosed in U.S.Pat. Nos. 4,535,278 and 4,555,650, for example.

[0003] A semiconductor device is typically produced by overlaying orsuperimposing a plurality of layers of circuit patterns on the wafer.The circuit pattern is first formed in a reticle and transferred into asurface layer of the wafer through photolithography. The layers ofcircuit patterns must be precisely aligned with one another duringprocessing. This requires precise alignment of the wafer and reticleduring the photolithography process. One source of alignment error isvibration of the structures within the photolithography system. Thereaction forces between the moving portion and fixed portion of themotor are often a source of vibrations in the system.

[0004] As the circuit density of integrated circuits increases andfeature size decreases, alignment errors must be further reduced oreliminated. Precise alignment of the overlays is imperative for highresolution semiconductor manufacturing.

[0005] There is, therefore, a need for a structure which isolates thevibrations induced by reaction forces generated by a motor to reduce oreliminate misalignment caused by the vibrations.

SUMMARY OF THE INVENTION

[0006] The present invention provides a structure for isolatingvibrations induced by reaction forces generated in a motor used toposition a reticle. A fixed portion of the motor, which is subject toreaction forces, is structurally isolated from the rest of the system inwhich the motor is operating.

[0007] An exposure apparatus of the present invention generally includesan optical system for imaging a pattern formed in a reticle onto anarticle, a reticle stage for supporting the reticle, and a motor forpositioning the reticle stage and reticle relative to the opticalsystem. The motor has a first portion and a second portion. The firstportion is connected to the reticle stage and movable relative to thesecond portion. The apparatus further includes a vibration isolationdevice configured to isolate vibration from reaction forces between thefirst and second motor portions.

[0008] The vibration isolation device may include structure which isstructurally independent of the first portion of the motor and connectedto the ground, for example. The vibration isolation device may furtherinclude a bearing for supporting the second portion of the motor toallow it to move in a direction opposite the first portion of the motorto counteract the reaction forces.

[0009] A flywheel may also be connected to the second portion of themotor to absorb rotational reaction forces created between the first andsecond motor portions.

[0010] In one embodiment, the exposure apparatus comprises a wafer stageand a wafer vibration isolation device configured for isolatingvibration from reaction forces between a magnet array and coil array ofa motor driving the wafer stage. The motor used to drive the reticlestage or wafer stage may be a planar motor or a linear motor.

[0011] A method of the present invention is for directing reactionforces created between first and second motor portions away from thefirst motor portion. The first motor portion is connected to a reticlestage for positioning a reticle relative to an optical system. Themethod comprises structurally isolating the second motor portion fromthe first motor portion to isolate vibration induced by the reactionforces created between the first and second motor portions.

[0012] The above is a brief description of some deficiencies in theprior art and advantages of the present invention. Other features,advantages, and embodiments of the invention will be apparent to thoseskilled in the art from the following description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic of a projection exposure apparatus with areaction force isolation system of the present invention.

[0014]FIG. 2 is an exploded view of one embodiment of a planar motorused in the exposure system of FIG. 1;

[0015]FIG. 3 is a schematic of a projection exposure apparatus with asecond embodiment of the reaction force isolation system of FIG. 1;

[0016]FIG. 4 is a schematic of a projection exposure apparatus with athird embodiment of the reaction force isolation system of FIG. 1;

[0017]FIG. 5 is a schematic of a projection exposure apparatus with afourth embodiment of the reaction force isolation system of FIG. 1;

[0018]FIG. 6 is a schematic of a projection exposure apparatus with afifth embodiment of the reaction force isolation system of FIG. 1;

[0019]FIG. 7 is partial schematic of a projection exposure apparatuswith a sixth embodiment of the reaction force isolation system of FIG.1;

[0020]FIG. 8a is a side view of a flywheel and rotary motor attached toa coil array of the projection exposure apparatus of FIG. 3; and

[0021]FIG. 8b is a perspective of the flywheel, rotary motor, and coilarray of FIG. 8a.

[0022] Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF THE INVENTION

[0023] Referring now to the drawings, and first to FIG. 1, a projectionexposure apparatus, generally indicated at 10, is shown. To illustratethe principles of the present invention, the isolation of vibrationsinduced by reaction forces generated by a motor is described inreference to a scanning-type photolithography system for substrateprocessing. However, it is to be understood that the present inventionmay be easily adapted for use in other types of exposure systems forsubstrate processing (e.g., projection-type photolithography system orelectron-beam (EB) photolithography system disclosed in U.S. Pat. No.5,773,837) or other types of systems (e.g., pattern position measurementsystem disclosed in U.S. Pat. No. 5,539,521, wafer inspection equipment,machine tools, microscope) for processing other articles in which thereduction of vibrations induced by reaction forces generated by a motoris desirable.

[0024]FIG. 1 is a schematic representation of a scanning-type exposuresystem 10 for processing a substrate, such as a wafer 12. In anillumination system 14, light beams emitted from an extra-high pressuremercury lamp are converged, collimated, and filtered into substantiallyparallel light beams having a wavelength needed for a desired exposure(e.g., exposure of photoresist on the wafer 12). In place of the mercurylamp, an excimer laser (Krf, Arf, or F2) can also be used. The lightbeams from the illumination system 14 illuminate a pattern formed in areticle 16 which is mounted on a reticle stage 18. The reticle stage 18includes an opening (not shown) to allow the light beams to pass throughthe stage. The stage may also be configured to support or retain thereticle along only one side of the reticle, for example. The light beamspenetrating the reticle 16 are projected on the wafer 12 via projectionoptics (lens) 24. The reticle stage 18 is movable in several degrees offreedom (e.g., three to six) by an actuator 31 which may be a linear orplanar motor as further described below. The reticle stage 18 issupported by bearings (not shown) on a reticle stage frame 40. Thesebearings may be air bearings, for example. An interferometer 34 ismounted on the reticle stage frame 40 and interacts with a mirror 35 tomeasure the position of the reticle 16 and provide a signal to a controlsystem 22, as is well known by those skilled in the art. The controlsystem 22 operates in conjunction with a drive system 20 and the motor31 to control the position of the reticle 16. The drive system 20provides the user with information relating to the position of thereticle 16.

[0025] The wafer 12 is positioned under the projection optics 24 andpreferably held by vacuum suction on a wafer holder (not shown) which issupported on a wafer stage 26. The wafer stage 26 is structured so thatit can be moved in several degrees of freedom (e.g., three to six) by aplanar motor 30 under precision control by a driver 32 and the systemcontroller 22, to position the wafer 12 at a desired position andorientation relative to the projection optics 24. The driver 32 providesthe user with information relating to X, Y, and Z positions as well asangular positions of the wafer 12. For precise positional information,an interferometer 36 and a mirror 37 are provided to detect the actualposition of the wafer 12. The signal from the interferometer 36 is fedto the control system 22 which acts with the driver 32 and motor 30 tocontrol the position of the wafer 12.

[0026] In operation, the light beams from the illumination system 14pass through the reticle 16 and expose photoresist on the wafer 12,which is supported and scanned using the wafer stage 26 driven by themotor 30. In the scanning-type exposure apparatus, the reticle 16 andthe wafer 12 are scanned and exposed synchronously (in accordance withthe image reduction in place) with respect to an illumination areadefined by a slit having a predetermined geometry (e.g., a rectangular,hexagonal, trapezoidal or arc shaped slit). This allows a pattern largerthan the slit-like illumination area to be transferred to a shot area onthe wafer 12. After the first shot area has been completed, the wafer 12is stepped by the motor 30 to position the following shot area to ascanning start position. This system of repeating the stepping andscanning exposure is called a step-and-scan system. The scan-typeexposure method is especially useful for imaging large reticle patternsor large image fields on the wafer 12, as the exposure area of thereticle 16 and the image field on the wafer are effectively enlarged bythe scanning process.

[0027] It is again noted that the configuration of the exposure system10 described above generally corresponds to a step-and-scan exposuresystem that is well known in the art. Further details of the componentswithin a scanning-type exposure apparatus may be referenced from U.S.Pat. Nos. 5,477,304 and 5,715,037, which are incorporated herein byreference in their entirety. It is to be understood that the presentinvention is not limited to wafer processing systems, or tostep-and-scan exposure systems for wafer processing. The generalreference to a step-and-scan exposure system is purely for illustratingan embodiment of an environment in which the concept of isolation ofmotor reaction forces to reduce system vibration may be advantageouslyadopted.

[0028] The components of the motor 30 used to move the wafer stage 26,are schematically illustrated in FIG. 2. The motor 30 is a planar motorcomprising an array of magnets (first motor portion) 56 and an array ofcoils (second motor portion) 50 having a plurality of coils 55 which areelectrically energized under control of the driver 32 (FIGS. 1 and 2). Aplate 52 is positioned above the coil array 50 to support the waferstage 26. The plate 52 is preferably made of nonmagnetic materials, suchas carbon fiber composites, plastics, ceramics including Zerodurceramics, A12O3 ceramics, and other suitable materials which do notimpair the magnetic flux of the magnets. The current distribution of thecoil array 50 interacts with a permanent magnetic field of the magnetarray 56 to cause a force between the magnet array and coil array. Theinteraction of the magnetic field and the current distribution permitsthe magnet array 56 to move with respect to the coil array 50 in atleast three, and preferably six degrees of freedom.

[0029] The motor 31 used to position the reticle stage 18 is similar tothe motor 30 described above. The planar motor includes a magnet array49 and a coil array 47 positioned adjacent to the magnet array andoperable to interact with magnetic fields of the magnet array to movethe reticle stage 18 (FIG. 1). The coil array 47 is attached to a lowersurface of reticle coil array frame 41 and the magnet array is attachedto an upper surface of the reticle stage 18, surrounding the reticle 16.

[0030] For simplicity, many details of the planar motor are omitted fromFIG. 2, as they alone do not constitute a part of the present invention.The planar motor may be a motor as described in pending U.S. patentapplication Ser. No. 09/192,813, by A. Hazelton et al., filed Nov. 16,1998, U.S. Pat. No. 09/168,694, by A. Hazelton et al. filed on Oct. 5,1998, and U.S. Pat. No. 09/135,624, by A. Hazelton, filed Aug. 17, 1999,for example. Structural details and operational principles of planarmotors are also disclosed in U.S. Pat. Nos. 4,535,278 and 4,555,650.Each of the above patents and patent applications are incorporatedherein by reference in their entirety. One or both of the motors 30, 31may also be a linear motor as described in U.S. patent application Ser.No. 09/219,545, by A. Hazelton et al., filed Dec. 22, 1998, for example.It is to be understood that the type of motor used to position eitherthe reticle stage 18 or the wafer stage 26 may be different than thosedescribed herein without departing from the scope of the invention.

[0031] Both motors 30, 31 cause a reaction force acting on the coilarrays 47, 50. As further described below, the reaction force isolationsystem of the present invention isolates these reaction forces from therest of the exposure apparatus.

[0032] The motors 30, 31 include magnet arrays 49, 56 which are attachedto the reticle stage 18 and wafer stage 26, respectively and are free tomove with the stages relative to the coil arrays 47, 50 (FIG. 1). Thismoving magnet embodiment is generally preferred over a moving coilarrangement when used in positioning devices, because the magnet arraysdo not require electrical current connections or cooling. However, it isto be understood that the coil arrays 47, 50 may also be attached to thestages 18, 26 and movable relative to fixed magnet arrays.

[0033] In the embodiment shown in FIG. 1, the illumination system 14,the reticle stage 18, and the projection optics 24 are separatelysupported by frames 38, 40, and 42, respectively. The frames 38, 40, 42are coupled to the ground (or other surface on which the overallexposure system is supported) through isolation system 60 and supports48. The projection optics frame 42 is mounted on the support 48 usingthe damping means 60. By providing the damping means 60 to couple theframes 38, 40, and 42 to the ground, any vibration that may be inducedby the reaction forces through the ground is isolated from the rest ofthe exposure system 10. The damping means 60 therefore, prevents thevibration of the ground from transmitting to the projection optics 24,the illumination system 14, the reticle 16, or the wafer 12. The dampingmeans 60 may include air or oil dampers, voice coil motors, oractuators, for example. Preferably, the damping means 60 includes anactuator (schematically shown at 61) to maintain the projection opticsframe 42 and the reticle coil array frame 41 level and preventmisalignment of the optical axes of the projection optics 24 and theillumination system 14. The actuator 30, 31 and positional feedbackscheme needed to achieve the leveling objective may be implemented usingsystems which are well known by those skilled in this art. Theillumination system and reticle stage frames 38, 40 are mounted on theprojection optics frame 42 to avoid the need for additional dampingmeans, since the damping means 60 isolates the combined frames 38, 40and 42. However, the illumination system and reticle stage frames 38, 40may also be individually coupled with ground.

[0034] The reticle stage 18 and wafer stage 26 are each supported bybearings (e.g., air bearings) on the reticle stage frame 40 and thesupport plate 52, respectively. The reticle stage frame 40 and thesupport plate 52 are both supported by the projection optics frame 42.The coil arrays 47, 50 are separately and rigidly coupled to the groundby fixed stands (vibration isolation devices) 63 and 62, respectively.When reaction forces are created between the coil arrays 47, 50 and themagnet arrays 49, 56, the reaction forces push against the ground.Because of the large mass of the ground, there is very little movementof the coil arrays 47, 50 due to the reaction forces. Since the reactionforces do not act on the frames 38, 40, and 42, vibration of the stages18, 26, illumination system 14 and lens 24 due to reaction forcesbetween the portions of the motor are substantially eliminated.

[0035] In a second embodiment of the present invention, generallyindicated at 65 and shown in FIG. 3, the support plate 52 and the coilarray 50 of the wafer motor 30 are supported by the projection opticsframe 42. The plate 52 is attached to mid sections of vertical members70 which depend from a horizontal member 45 of the projection opticsframe 42. A horizontal support platform 72 is attached to opposite endsof the vertical members 70. The coil array 50 rides on a vibrationisolation device comprising bearings 74 (e.g., air bearing or ballbearings) which move upon the horizontal support platform 72. In thisembodiment, the reaction forces cause the coil array 50 to move sidewayson the bearings 74, thus absorbing the reaction forces with its inertia.The reaction forces are absorbed by this inertia, since the reactionforces are very small compared to the weight of the system thatcomprises the projection optics 24, wafer stage 26, reticle stage 18,and illumination system 14. The invention of FIG. 3 uses the principleof momentum conservation, so the center of gravity of the system 10 doesnot shift according to the position of the wafer stage 26. Therefore thedamping means 60 of this invention do not require an actuator 61 asprovided in the first embodiment shown in FIG. 1.

[0036] Similar to the wafer stage 26 described above, the reticle stage18 is supported by bearings (not shown) on a support plate 82 which isconnected to the reticle stage frame 40. The coil array 47 rides onbearings 84 (e.g., air bearing or ball bearings) on the reticle stageframe 40. The magnet array 49 is mounted on a lower surface 88 of thereticle stage 18. The coil array 47 is positioned adjacent to the magnetarray 49 to interact with magnetic fields of the magnet array to movethe reticle stage 18. The reaction forces cause the coil array 47 tomove on the bearings 84, thus absorbing the reaction forces with itsinertia. As the reticle stage 18 is forced in one direction, the coilarray 47 freely moves in the opposite direction due to the conversationof momentum principle. Thus, the force is transferred to the inertia ofthe moving coil array 47 and not to the body of the exposure apparatus.

[0037] A flywheel, indicated schematically at 90 in FIG. 3, may also beattached to one or both of the coil arrays 47, 50 to absorb torsionalforces and prevent rotation of the coil array. A rotary motor 110 ispreferably interposed between the coil array 47, 50 and the flywheel 90to rotate the flywheel and counteract the torsional forces (FIGS. 3, 8a,and 8 b). The angular momentum on the coil array 47, 50 with the rotarymotor 110 and flywheel 90 attached to the coil array can be calculatedas:

∫Tdt=(J _(c) +J _(f))ω_(c) +J _(f)ω_(cf)=0 (for sufficiently large t)

[0038] where:

[0039] T=Torque on coil array;

[0040] J_(c)=mass moment of inertia of coil array;

[0041] J_(f)=mass moment of inertia of flywheel;

[0042] ω_(c)=angular velocity of coil array; and

[0043] ω_(cf)=angular velocity of rotary motor (which is equal to theangular velocity of the coil array relative to the flywheel).

[0044] The rotary motor 110 thus rotates at a speed ω_(cf) to rotate theflywheel 90 at an appropriate speed to compensate for the torsionalforces on the coil array 47, 50 and prevent rotation of the coil array.The angular velocity of the rotary motor ω_(cf) should be sufficientlylarge so that the angular velocity of the coil array ω_(c) is small. Therotary motor 110 is preferably driven by a controller (not shown) whichmonitors the angular rotation of the coil array 47, 50.

[0045] In a third embodiment, generally indicated at 95 and shown inFIG. 4, the plate 52 is supported on support posts 54 which projectthrough clearance holes in the coil array 50. The support posts 54 reston a base 58 to shorten the length of the posts and prevent the postsfrom bending. The plate 52 and the support posts 54 may be formedseparately or formed as a unitary structure. The base 58 is coupled tothe ground by damping means 60, such as air or oil dampers, voice coilmotors, actuators, or other known vibration isolation systems. Theillumination system, reticle stage and projection optics frames 38′,40′, and 42′ may also be coupled to the ground by similar damping means.The coil array 50 is separately and rigidly coupled to the ground byfixed stands (vibration isolation device) 62. In this embodiment, whenreaction forces are created between the coil array 50 and the waferstage 26, the reaction forces push against the ground. Because of thelarge mass of the ground, there is very little movement of the coilarray 50 from the reaction forces. By providing damping means 60 tocouple the base 58 and the illumination system, reticle stage, andprojection optics frames 38′, 40′ and 42′ to the ground, any vibrationthat may be induced by the reaction forces through the ground isisolated from the rest of the exposure apparatus.

[0046] A fourth embodiment, generally indicated at 98, is shown in FIG.5. The fourth embodiment is similar to the third embodiment 95, exceptthat instead of rigidly coupling the coil array 50 to the ground, abearing coupling (vibration isolation device) 64 is used. The bearingcoupling may be a planar (X, Y, and Theta Z) journal bearing 64positioned at the end of supports 66 coupled to the coil array 50, forexample. Ball bearings or air bearings may also be used. When reactionforces are created between the magnet array 56 and the coil array 50,the wafer stage 26 and the coil array move in opposite directions andthe coil array absorbs the reaction forces. The mass of the coil array50 is typically substantially larger than that of the wafer stage 26.Consequently, in accordance with conservation of momentum, the movementof the coil array 50 caused by the reaction force is typicallysubstantially smaller than the movement of the wafer stage 26 under thesame reaction force. It is to be understood that in the embodiment ofFIG. 5, the damping means 60 may be omitted if the bearing support 64,66 can effectively isolate all reaction forces that may inducevibrations in the rest of the exposure apparatus.

[0047] In a fifth embodiment of the present invention generallyindicated at 102 and illustrated in FIG. 6, the coil array 50 is rigidlysupported on the ground by supports (vibration isolation device) 62. Inthis embodiment, instead of supporting the plate 52 of the planar motor30 on support posts 54 on the base 58, as was done in the earlierembodiment (shown in FIG. 4), the plate 52 is supported by theprojection optics frame 42′. The plate 52 is preferably formed with athick honeycomb structure or other type of reinforced structure toprevent it from bending. The projection optics frame 42′ is isolatedfrom vibration transmitted through the ground by a damping means 60.

[0048]FIG. 7 shows a sixth embodiment, generally indicated at 104. Themotor 30 includes a cooling platform 76 which is supported by ahorizontal support platform 72. The cooling platform 76 includesconduits 78 through which coolant 77 can pass through. Alternatively,Peltier cooling or ventilating air cooling may be deployed. The waferstage plate 52 is supported on stands 80 which are supported on thecooling platform 76. The cooling platform 76 provides a support surfaceon which the coil array 50 rests on bearings 74. The wafer stage 26further includes a leveling stage 83 which positions the wafer 12 inthree additional degrees of freedom. The leveling stage 83 has at leasttwo actuators 94 (e.g., voice coil motors) which actuate in thedirection of axis A of projection optics 24 in accordance with focussensors 92 a and 92 b. One focus sensor 92 a emits a focusing beam tothe wafer 12 and the other focus sensor 92 b receives the reflected beamfrom the wafer 12. The leveling stage 83 adjusts the focal plane of theprojection optics 24 to align with the surface of the wafer 12. It ispreferable that the leveling stage 83 be structurally isolated (withoutmechanical contact) from the wafer stage 26 so that vibration of thewafer stage 26 (e.g., caused by the air bearing) may be isolated.Additionally, a cooling system such as described in U.S. patentapplication Ser. No. 09/259,465, by A. Hazelton et al., filed Feb. 26,1999, may be used as the above described cooling system to cool the coilarray 50 of the motor 30.

[0049] It is to be understood that the vibration isolation devices shownin the third, fourth, fifth, and sixth embodiments to isolate vibrationfrom the wafer stage 26, may also be incorporated in the reticle stage18, as described above for the first and second embodiments. Further,any combination of vibration isolation devices may be used for thereticle and wafer stages 18, 26, or a vibration isolation device may beused only for the reticle stage or the wafer stage, for example.

[0050] While the invention has been described with respect to thedescribed embodiments in accordance therewith, it will be apparent tothose skilled in the art that various modifications and improvements maybe made without departing from the scope and spirit of the invention.For example, in the above embodiments of FIGS. 4, 5, and 6, theillumination system, reticle stage, and projection optics frames 38, 40,and 42 are separately coupled to the ground. Alternatively, theillumination system and reticle stage frames 38 and 40 may be mounted onthe projection optics frame 42 without damping means as in FIGS. 1 and3. Conversely, the illumination system, reticle stage, and projectionoptics frames 38, 40 and 42 in the embodiments of FIGS. 1 and 3 may beseparately supported on damping means as in FIGS. 4, 5, and 6.Additionally, various combinations of damping means and bearing supportmay be deployed to provide the reaction force isolation function, or toprovide redundancy in such function. Further, the present invention maybe adopted in other types of exposure apparatus and other types ofprocessing systems in which precision positioning utilizing a motor isdesired. While the described embodiments illustrate planar motors usedin an X-Y plane, planar motors used in other orientations and more orless dimensions may be implemented or linear motors may be used with thepresent invention.

[0051] The photolithography system according to the present imbodimentis also applicable to a step-and-repeat type photolithography systemthat exposes a mask pattern while a mask and a substrate are stationaryand the substrate is moved in step in succession. Alternatively, thephotolithography system according to the present invention may be usedfor a proxomity photolithography system that exposes a mask pattern byclosely locating a mask and a substrate without the use of e projectionoptical system.

[0052] The light source for the photolithography system of the presentinvention is not limited to the use of g-line (436 nm), i-line (365 nm),KrF excimer laser (248 nm), ArF excimer laser (193 nm) and F₂ laser(157nm). Charged particle beams such as x-rays and electron beams can beused. for instance, in the case where an electron beam is used,thermionic emission type lanthanum hexaboride (LaB₆) or tantalum (ta)can be used as an electron gun. Furthermore, in the case where anelectron beam is used, the structure could be such that either a mask isused or a pattern can be directly formed on a substrate without the useof a mask.

[0053] When far ultra-violet rays are used, such as those emitted by theexcimer laser, the glass material of the projection optical system ispreferably quartz or fluorite glass. These materials are well suited forthe transmission of far ultra-violet rays. Further, when the projectionoptical system employs an F₂ laser or x-ray, the optical alignmentchosen should be either catadioptric or refractive (and include areflective reticle.) The preferred projection optical system forelectron beams includes electron lenses and deflectors; and the opticalpath for electron beams should be in a vacuum. In any instance, themagnification for projection optical system is not limited to areduction system, but can include a lx or higher magnification system aswell.

[0054] The assembly of the photolithography system described hereinrequires the integration of various described subsystems. Duringassembly, each subsystem has a prescribed mechanical accuracy,electrical accuracy, and optical accuracy that must be maintained. Inorder to maintain these accuracies prior to and following assembly,every optical system is adjusted to achieve its optical, mechanical, andelectrical accuracy before and after assembly. The process of assemblingeach subsystem into a photolithography system includes assembly of themechanical interface, electrical circuits and air pressure plumbingconnections between each subsystem. Once fully assembled and theaccuracies of each subsystem have been verified, the accuracy of thesystem as a whole is checked and verified. Preferably, assembly andaccuracy analysis should occur in a clean room where temperature andpossible contamination can be tightly controlled.

[0055] To manufacturer a semiconductor device using the photolithographysystem of the present invention, the device's function and performancecriteria must first be established. Based on these criteria, a mask(reticle) is designed and a wafer is made from a silicon material.Finally, the reticle pattern is exposed on the wafer and, thereafter,the semiconductor device is assembled. Those skilled in the art willrecognize that the final assembly of a semiconductor device includessuch steps as dicing, bonding, and packaging. The completedsemiconductor device is then inspected to ensure that it meets theoriginal perfomance and function criteria as well as any quality controlcriteria.

[0056] In view of the above, it will be seen that the several objects ofthe invention are achieved and other advantageous results attained.

[0057] As various changes could be made in the above constructions andmethods without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:
 1. An exposure apparatus comprising: an opticalsystem for imaging a pattern formed in a reticle onto an article; areticle stage for supporting the reticle; a motor for positioning thereticle stage and reticle relative to the optical system, the motorhaving a first portion and a second portion, the first portion of themotor being connected to the reticle stage and movable relative to thesecond portion of the motor; and a vibration isolation device configuredto isolate vibration resulting from reaction forces created between thefirst and second motor portions.
 2. The exposure apparatus of claim 1wherein the first motor portion is supported by a stationary support andthe second motor portion is supported by the vibration isolation devicewhich is structurally independent of the stationary support.
 3. Theexposure apparatus of claim 2 wherein the vibration isolation device isconnected to the ground.
 4. The exposure apparatus of claim 2 whereinthe vibration isolation device comprises a bearing configured to allowthe second motor portion to move in a direction opposite the first motorportion upon application of the reaction force to the second motorportion.
 5. The exposure apparatus of claim 4 wherein the bearingcomprises an air bearing.
 6. The exposure apparatus of claim 4 whereinthe bearing comprises a ball bearing.
 7. The exposure apparatus of claim2 wherein the stationary support comprises a damper.
 8. The exposureapparatus of claim 1 wherein the motor comprises a planar motor.
 9. Theexposure apparatus of claim 1 wherein the motor comprises a linearmotor.
 10. The exposure apparatus of claim 1 wherein the first motorportion comprises a magnet array and the second motor portion comprisesa coil array.
 11. The exposure apparatus of claim 10 wherein thevibration isolation device comprises a frame extending from the groundto a location above the reticle stage and wherein the magnet array isconnected to an upper surface of the reticle stage and the coil array isconnected to the frame at a location above the reticle stage.
 12. Theexposure apparatus of claim 4 further comprising a flywheel connected tothe second portion of the motor for absorbing rotational reaction forcescreated between the first and second motor portions.
 13. The exposureapparatus of claim 1 wherein the article is a wafer.
 14. The exposureapparatus of claim 13 further comprising a wafer stage for supportingthe wafer and a wafer stage motor for positioning the wafer stage, thewafer stage motor having a coil array and a magnet array, one of thecoil array and the magnet array being connected to the wafer stage andmovable relative to the other of the coil array and the magnet array,and a wafer vibration isolation device configured for isolatingvibration from reaction forces between the magnet array and the coilarray.
 15. The exposure apparatus of claim 14 wherein the wafer stagemotor is a planar motor.
 16. The exposure apparatus of claim 14 whereinthe magnet array is connected to the wafer stage.
 17. The exposureapparatus of claim 1 further comprising a controller for controlling theposition of the reticle stage.
 18. The exposure apparatus of claim 17further comprising an interferometer, for providing information on thelocation of the reticle stage to the controller.
 19. The exposureapparatus of claim 14 wherein the wafer stage coil array is supported ona platform having a coolant flowing therethrough.
 20. A method ofdirecting reaction forces created between first and second motorportions away from the first motor portion, the first motor portionbeing attached to a reticle stage for positioning a reticle relative toan optical system, the method comprising structurally isolating thesecond motor portion from the first motor portion to isolate vibrationinduced by reaction forces created between the first and second motorportions.
 21. The method of claim 20 wherein the step of structurallyisolating the second motor portion from the first motor portioncomprises supporting the first motor portion by a stationary support andconnecting the second motor portion to a frame connected to the groundand structurally independent of the stationary support.
 22. The methodof claim 20 wherein the step of structurally isolating the second motorportion from the first motor portion comprises supporting the secondmotor portion on a bearing so that the second motor portion is free tomove in a direction opposite the first motor portion.
 23. The motorportion of claim 22 further comprising connecting a flywheel to thesecond motor portion to absorb rotational reaction forces createdbetween the first and second motor portions.